Long-chain fatty acids are the major substrates for energy generation in the heart.1 Before entering the mitochondrial P-oxidation cycle, long-chain fatty acids have to be transported across the mitochondrial membranes as carnitine esters. The machinery needed for transport of long-chain acylcarnitines includes three membrane-associated components:2 the enzyme carnitine palmitoyltransferase 1 (CPT1), the carrier carnitine acylcarnitine-translocase (CACT), and the enzyme carnitine palmitoyltransferase 2 (CPT2). Of CPT1, two isoforms are expressed in the neonatal heart: L-CPT1 (the "liver-type" isoform) and M-CPT1 (the "muscle-type" isoform).3 These isoforms are encoded by two separate genes,4,5,6 CPT1A and CPT1B, respectively.

Several familial cardiomyopathies are known to be associated with deficiencies in long-chain fatty acid transport and oxidation.7,8,9 Patients with adult10,11 and juvenile presentations of CACT- and CPT2 deficiencies have been described, of which the acute juvenile forms are accompanied by severe cardiac problems.12,13,14,15,16 Of CPT1 deficiencies,

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